1. Field of the Invention
The present invention relates to a technology of controlling a pressure of fuel supplied to an engine.
2. Description of the Related Art
There is described as a fuel supply apparatus which supplies fuel from a fuel tank to a fuel injection valve by a fuel pump as described in Japanese Unexamined Patent Publication No. 11-247695.
In the fuel supply apparatus, feedback control in which a target current is set in accordance with a target fuel pressure, and a driving current of the fuel pump is made to coincide with the target current is carried out.
By the way, in a conventional fuel supply apparatus, means for actively lowering a fuel pressure is not provided.
Therefore, for a request to lower a fuel pressure, there has been no means but to wait for that the fuel is removed from a fuel pipe due to the fuel injection from the fuel injection valve.
Accordingly, under the condition that a fuel injection quantity is little, such as a time when fuel injection is resumed from a state in which fuel is cut during deceleration state, or the like, it takes a long time that a fuel pressure higher than a target falls to the target.
Then, when a fuel pressure is higher than a target, in some cases, the combustibility deteriorates due to the injection characteristic from the fuel injection valve being varied. Further, when a fuel pressure is higher than a target, in some cases, a precision in measuring the fuel deteriorates, and the emission increases due to a fuel injection time being made short.
Here, when a route for returning fuel from the fuel pipe to the fuel tank is provided in order to actively lower a fuel pressure, there is the problem that the cost of the fuel supply apparatus rises.